1. Field of the Invention
This invention relates to polymerizable compositions for use in or as adhesives, sealants and/or coatings. The compositions include a (meth)acrylate component together with a dye substantially dissolved in the (meth)acrylate component which imparts a first color to said (meth)acrylate component. Upon curing, a resultant cured composition has a second color. The invention also relates to a method of detecting substantially full cure of the compositions.
2. Brief Description of Related Technology
Fluorescing agents have been incorporated into curable compositions to provide a non-destructive method for inspection, to identify the presence of cured films, and to ensure proper coverage of the coating on an article. Heretofore, the addition of the fluorescing agent, however, does not provide a change in color to determine whether the composition has fully cured; rather the fluorescing agent provided fluorescence.
Analytical instrumentation has been developed for determining cure on production lines. However, such instrumentation is expensive and oftentimes impractical due to floor space constraints in the manufacturing environment.
U.S. Pat. No. 5,707,781 (Wilczak) discloses a photopolymerizable composition having one or more acyl or diacyl phosphine oxide photoinitiators in combination with a fluorescent optical brightener. The fluorescent optical brighteners enhances the photosensitivity of the acyl or diacyl phosphine oxide photoinitiators. The disclosed composition is not reported to substantially change color on exposure to actinic radiation when used, such as in the top layer of a color proofing element to remedy unwanted discoloration.
U.S. Pat. No. 6,080,450 (Cantor) describes the use of a UV/VIS (ultra violet/visible) phosphine oxide photoinitiator to cure a polymerizable acrylate formulation, with the presence of a fluorescing agent to confer a visible response.
U.S. Pat. No. 5,302,627 (Field) reports the addition of a dye to UV radiation curable silicone-containing polymeric compositions which contain photoinitiators. Upon exposure to UV radiation, the silicone-containing polymeric composition undergoes a color change indicating that the composition has cured. The dyes used include an anthraquinone dye having a Color Index Solvent Blue 104, 1-hydroxy-4-[(methylphenyl)amino]-9,10-anthracenedione, and an azo dye mixture of azo benzene azo naphthyl benzene amine alkyl/alkoxy derivatives having a Color Index Solvent Blue 99, and azo benzene azo naphthyl benzene amine alkyl derivatives having a Color Index Solvent Red 166. Large amounts of the dye, greater than 30 ppm based on the weight of the composition, are reported to inhibit cure.
U.S. Pat. No. 6,017,983 (Gilleo) appears to refer to the use of a diazo dye that is believed to form a salt or complex with acid anhydrides, which acts as a color indicator for particular anhydride/epoxy resin thermoset adhesives. The resulting salt or complex is reported to produce a chromophoric shift in the dye which is indicative of the amount of acid anhydride present, and hence, the degree of cure. As the epoxy resin cures, the amount of acid anhydride diminishes, thus, producing a color change. This system appears to be limited to acid anhydride hardeners used to cure epoxy resins.
U.S. Pat. No. 6,312,644 B1 (Moriarty) appears to teach the use of pyranine fluorescent monomers for tagging polymers used in industrial waste water treatment systems as a means for determining the amount of the polymer treatment agent. The fluorescence of the polymer is a direct measure of the concentration of the tagged polymer in the water. Thus, a real time in situ decline in the fluorescence indicates that a non-desired event such as scaling is occurring.
Notwithstanding the state of the technology, it would be desirable to provide a (meth)acrylate composition that demonstrates “self-indicating” capabilities to detect when cure has been achieved.